\(A=\left(-\dfrac{3}{11}\right).\left(\dfrac{11}{-3}\right).\left(\dfrac{7}{10}.\left(-20\right)\right)=1.\left(-14\right)=-14\\ E=\left(\dfrac{31}{15}.\dfrac{3}{19}.\dfrac{2}{13}\right):\left(-\dfrac{5}{19}\right)=\left(\dfrac{3}{19}.\dfrac{2}{13}\right):\left(-\dfrac{5}{9}\right)=\dfrac{6}{247}:\left(-\dfrac{5}{9}\right)=\dfrac{6}{247}.\dfrac{-9}{5}=\dfrac{-54}{1235}\)

bạn đưa hình vẽ luôn đc ko

B

câu b qua gì vẽ đg thẳng

\(a,=\sqrt{49-5.4\sqrt{6}}-\sqrt{49+5.4\sqrt{6}}=\sqrt{49-20\sqrt{6}}-\sqrt{49+20\sqrt{6}}=\sqrt{49-2.2\sqrt{6}.5}-\sqrt{49+2.2\sqrt{6}.5}=\sqrt{\left(2\sqrt{6}-5\right)^2}-\sqrt{\left(2\sqrt{6}+5\right)^2}=\left|2\sqrt{6}-5\right|-\left|2\sqrt{6}+5\right|=5-2\sqrt{6}-2\sqrt{6}-5=-4\sqrt{6}\)

Câu b hình như sai đề

\(15-\left(30+x\right)=x-\left(27-8\right)\\ 15-\left(30+x\right)=x-19\\ \left(30+x\right)=15-x+19\\ 30+x=-x+34\\ 30+x+x-34=0\\ 2x-4=0\\ x=2\)

Ta có  góc B - góc a = 70

=> góc a = góc B - 70

ta có B + D = 200

=> góc D = 200 - góc B

Xét tg abcd có

góc a + góc B + góc C + góc  D =360 ( tổng 4 góc trong tg)

góc B - 70 + góc B + góc B - 70 + 200-góc B =360

2 góc B + 60 = 360

=> 2 góc B = 300

góc B =150

=> góc a = góc C 150 - 70 = 80 độ 

góc D = 200 - 150 = 50

\(\text{a},=\dfrac{1}{1.2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+...+\dfrac{1}{9.10}+\dfrac{1}{10.11}\\ =1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+....+\dfrac{1}{9}-\dfrac{1}{10}+\dfrac{1}{10}-\dfrac{1}{11}\\ =1-\dfrac{1}{11}=\dfrac{11-1}{11}=\dfrac{10}{11}\)

\(=\left(-\dfrac{5}{7}\right)\left(\dfrac{4}{13}+\dfrac{9}{13}\right)+\left(-\dfrac{2}{7}\right)=\left(-\dfrac{5}{7}\right).\left(\dfrac{13}{13}\right)+\left(-\dfrac{2}{7}\right)=\left(-\dfrac{5}{7}\right)+\left(-\dfrac{2}{7}\right)=-1\)

D